Fluid pulse width modulator



Oct. 4, 1966 E. E. METZGER 3,2 76,464

FLUID PULSE WIDTH MODULATOR Filed Oct. 21, 1965 I NVENTOR.

fE/c E. METZGEE 3 Sheets-Sheet 1 Filed Oct. 21, 1965 Oct. 4, 1966 E. E. METZGER 3,276,464

FLUID PULSE WIDTH MODULATOR 5 Sheets-Sheet 2 INVENTOR ERIC E. METZGER BY w ATTOR NEYS Oat, 4, 1966 E. E. METZGER FLUID PULSE WIDTH MODULATOR 3 Sheets-Sheet 5 Filed Oct. 21, 1965 INVENTOR Ezlc E. METZGER ATTORNEYS United States Patent 3,276,464 FLUID PULSE WIDTH MODULATOR Eric E. Metzger, Silver Spring, Md, assignor to Bowles Engineering Corporation, Silver Spring, Md, a corporation of Maryland Filed Oct. 21, 1965, Ser. No. 505,593 17 Claims. (Cl. 137--81.5)

This application is a continuation-in-part of US. application Serial No. 299,740 filed August 5, 1963, in the name of Eric E. Metz'ger and entitled, 'Fluid Pulse Width Modulator, now abandoned.

This invention relates to accelerometers in general and, more specifically, to a pure fluid accelerometer.

In one form of the present invention, the pure fluid accelerometer of this invention comprises a pure fluid oscillator either self or externally excited incorporating a pure fluid amplifier for providing the necessary gain to the device. In this embodiment, the apparatus provides a pulse width modulated output signal.

In order to more clearly understand the nature and scope of the instant invention, it is initially described as applied to an oscillator employing a pure fluid amplifier of the boundary layer type.

In boundary layer types of pure fluid amplifiers, a high energy power jet is directed towards a particular target area of a receiving aperture system by the pressure distribution in the power jet boundary layer region. This pressure distribution is controlled by the wall configuration of the interaction chamber, the power jet energy level, the fluid transport characteristics, the backloading of and on the amplifier output passages, and the flow of control fluid to the power jet boundary layer region. Whereas sidewalls are not essential for a stream interaction type fluid amplifier, a boundary layer control fluid amplifier generally uses the sidewalls for deflection of the power jet. In a boundary layer control fluid amplifier, special design of the interaction chamber configuration provides units wherein the power jet will lock-on to one sidewall and remain in the locked-on flow configuration without a control fluid flow. When the power jet is suitably deflected by a control fluid flow, it can lock-on to the opposite sidewall and remain in the lock-0n flow configuration even after the control fluid flow is stopped. Thus, this unit possesses positive feedback; however, the feedback path is created and destroyed each time the power jet is deflected to another position. The feedback path is a flow pattern within the interaction chamber governed by the chamber configuration and the power jet flow.

The boundary layer type of fluid amplifier described briefly hereinabove basically controls the delivery of energy, pressure, or mass flow of a main stream of fluid to an outlet orifice or utilization device by means of control fluid flow issuing from a control nozzle generally at right angles to the main stream. The proportion of the relatively high energy main stream delivered to an orifice may be varied as a linear or non-linear function of the relatively low energy of a control stream interacting therewith. Since the energy controlled is larger than the control energy supplied, an energy gain is realized and amplification in the conventional sense is realized. Such amplifiers require no moving parts other than the fluid flow therein and consequently have a frequency response considerably higher than prior art fluid systems which employ moving parts.

Fluid oscillators require, in addition to fluid amplifiers, some means for storing energy and feeding back in proper phase a portion of the stored energy to the amplifier. The oscillators which may be constructed in accordance with the teachings of this invention may store fluid energy in one or both of two forms, potential energy and kinetic energy. Potential energy is energy associated with a fluid capacitance. The term fluid capacitance, as used hereafter, is defined as that class of fluid energy storage means which stores fluid potential energy. In general, the energy stored in a fluid capacitance increases as a result of introduction of additional fluid therein. A fluid capacitance may take one or more of the following forms: compression of the fluid to a greater density, change of thermodynamic state of the fluid, change of elevation of the fluid, change of fluid internal energy level, compression of a second fluid separated from the first fluid by a flexible wall, compression of a second fluid in contact with the first fluid, deformation of elastic walls which restrain the fluid, change of elevation of a weight supported by the fluid, and compression of bubbles or droplets of one fluid entrained in another.

Fluids in motion have a kinetic energy Which represents a second form of stored energy. The method of storing energy in this form is to accelerate the fluid to a higher speed. Fluid inertance is a measure of the pressure required to accelerate a mass of a fluid in a passageway, and is usually associated with fluid flow through a tube.

The term fluid includes compressible as well as incompressible fluids, fluid mixtures and fluid combinations. When compressible fluids are used the fluid energy storage means need not be resilient or expansi'ble, but may be made of rigid metal or plastic or any other inflexible or non-resilient material. If the fluid is incompressible then the fluid storage means should be made elastically deformable or should have a free surface such as water in a reservoir. A pressure-loaded flexible diaphragm can be provided in a fluid capacitance if it is not feasible to provide an elastically deformable container, reservoir or tank. A loaded piston is one type of elastically deformable tank.

The rate of oscillation of this type of oscillator varies with the rate at which the capacitance or inertance fills and discharges, and therefore this type of oscillator is known to those working in the art as a relaxation type of pure fluid oscillator.

US. Patent No. 3,016,066 to Raymond W. Warren discloses an oscillator utilizing a boundary layer type of pure fluid amplifier to effect the requisite power gain, and is generally known to those working in the art as a sonic oscillator, as distinguished from the aforedescribed relaxation type of oscillator.

In accordance with the principles and teachings of the instant invention either type of pure fluid oscillator may be constructed to provide a pulse modulated oscillator. A pulse modulated oscillator is an oscillator which produces constant frequency pulses but the width of the pulses vary in accordance with the angular acceleration imparted to the modulator.

The molulator comprises, in one form, a pure fluid oscillator of the sonic type disclosed above including a pure fluid amplifier of the boundary layer type provided with a coil, or a portion thereof, in the fluid feedback path or loop. When the molulator is rotated about an axis at an angle to the plane of the coil, a flow of fluid is established in the loop in a direction opposite to the direction of rotation of the body. This flow during one-half cycle aids flow of fluid in the feedback path and during the other half cycle retards flow on the feedback path, all in accordance with the angular acceleration of the oscillator. As a result, the output fluid pulses from the oscillator are correspondingly acceleration modulated.

In a second embodiment of the present invention, the mean position of the power stream of an internally or externally driven oscillator is modified by means of fluid flow in a loop lying in a plane at an angle to the direction of angular acceleration of the device. The loop is con- 3 nected between opposed control nozzles of an analog amplifier forming a part of the oscillator circuit. Flow of fluid through the loop due to angular acceleration biases the power stream and again produces pulse width modulation.

In a third embodiment of the invention, the mean position of the power stream of a pure fluid analog amplifier is varied with angular acceleration so that the differential output signal is a function of angular acceleration.

It is therefore broadly an object of this invention to provide a pure fluid accelerometer.

More specifically, it is an object of this invention to provide a feedback loop for a pure fluid oscillator, the feedback loop being designed so that when the oscillator is rotated about a prescribed axis, a modulated fluid output signal issues from the oscillator, the output signal being a function of the angular acceleration and direction of rotation of the oscillator.

Another object of the present invention is to provide a pure fluid accelerometer employing an analog amplifier, the mean position of the power stream of which is a function of fluid flow induced by angular acceleration in a loop, lying at an angle to the axis of acceleration, extending between opposed control nozzles of the amplifier.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 illustrates a side view of the pure fluid pulse modulator constructed in accordance with this invention;

FIGURE 2 is a plan view of the fluid pulse modulator illustrated in FIGURE 1;

FIGURE 3 illustrates typical fluid output pulses which might be generated by a prior art pure fluid oscillator;

FIGURE 4 illustrates typical pulse modulated fluid signals generated by the system of the present invention;

FIGURE 5 illustrates a fluid pulse modulator mounted for rotation in a rotatable body;

FIGURE 6 is a front view of a second embodiment of the present invention; and

FIGURE 7 is a front view of another embodiment of the present invention.

Referring now to FIGURE 1 for a more complete understanding of the present invention, there is shown one embodiment of a pulse modulating system 10 which comprises basically a pure fluid amplifier 11 and a feedback loop 30 formed with a coil 31. Although coil 31 is shown having one convolution, it is understood that this is only for the purpose of illustration and that coil 31 may, for example, have more than one convolution or, alternatively, have only a portion of a convolution. For example, coil 31 may have only one-half of a convolution. It should be further understood that the present invention is not limited to any particular configuration, or shape, of the feedback path; a coil, or convolution, merely being exemplary of one embodiment of the invention. How ever, the necessary relationships between the plane of the feedback path and the axis of rotation of the system will hereinafter be described.

The pure fluid amplifier 11, which is preferably of the boundary layer type, embodied in the pulse modulator 10 may be formed by molding or etching out the configuration shown in FIGURE 1 in a plate 12 which is sandwiched between a pair of flat plates 13a and 13b, the plates 12, 13a and 13b being sealed in a fluid-tight relationship one to the other by adhesives, machine screws, or other suitable means.

The amplifier 11 comprises a power nozzle 14, substantially opposed control nozzles 15 and 16, an interaction chamber 17 for receiving the power and control streams, output passages 18 and 19, respectively, positioned downstream of the chamber 17 for receiving fluid from the chamber 17, and output tubes 20 and 21 for receiving fluid output signals from the output passages 18 and 19, respectively. A tube 28 is threadedly connected to the plates 12, 13a and 13b to supply fluid for the power stream which issues from the power nozzle. The ends of the feedback loop or delay line 30 are threadedly connected in the plates 12, 13a and 13b to the input ends of the nozzles 15 and 16 so that fluid can flow through the loop 30 and supply control streams or pulses to the control nozzles 15 and 16.

In the system 10 illustrated in FIGURES 1 and 2 and using water as the working fluid, the width of the orifices of the control nozzles 15 and 16 are shown to be three times the width of the power nozzle orifice, although it should be understood that these dimensions are not critiical and are merely exemplary of one specific design of modulator. The walls 32 and 33 forming opposite sidewalls of the interaction chamber 17 are set back a predetermined distance from the orifice of the power nozzle 14 so that points of wall attachment are created between fluid from the power nozzle 14- and either sidewall 32 or 33, depending upon the direction of power stream displacement by fluid from the control nozzles 15 and 16.

If it is assumed, for example, that the fluid power stream issuing from the nozzle 14 has attached itself to the sidewall 33, the stream may be displaced from the sidewall 33 and attach itself onto the sidewall 32 as a result of the control nozzle 16 issuing a fluid stream into the boundary layer region between the power stream and the sidewall 33. Conversely, fluid from the control nozzle 15 will displace the power stream flowing against the sidewall 32 until it reattaches to the sidewall 33, assuming the quantity of fluid issuing from the control nozzle 15 is greater than the quantity issuing from the control nozzle 16.

If the control nozzles 15 and 16 were connected by a single loop in a plane parallel to the plane of the amplifier 11, as disclosed in U.S. Patent No. 3,016,066; or if a conventional relaxation type of a pure fluid oscillator is used, the fluid output signals would typically be substantially symmetrical fluid pulses, the peaks and bases of the pulses being of approximately the same width as illustrated in FIGURE 3 of the accompanying drawings. Substantially symmetrical fluid pulses would be produced, even though an angular acceleration was applied to the devices about an axis corresponding to the axis shown in FIG- UR'E 5.

Refer-ring now to FIGURE 4, there is shown typical modulated pulses produced by an oscillator having a coil such as the coil 31, FIGURES l and 2, in the feedback path or feedback loop of the oscillator. As will be evident from the subsequent and more detailed disclosure of this invention, if the oscillator is rotated about an axis at an angle to the axis of the coil, or if the coil is planar and the oscillator is rotated about an axis essentially perpendicular to the plane of the coil, the widths of, for instance, the positive peaks of the fluid output pulses vary in a sense and to an extent which are relatively functions of direction and the angular acceleration of the unit respectively. Thus, by the relatively simple expedient of forming a coil in a feedback path or loop of any of the known prior art pure fluid amplifiers, it is possible to make the resulting system sensitive to the angular acceleration of the oscillator. Furthermore, it is not necessary that there be a complete coil, or convolution, in the feedback path, since the system will be sensitive to the angular acceleration of the oscillator when only a portion of the feedback path is outside the plane formed by the amplifier 11; that is, angular acceleration of the system about an axis will modulate the fluid output pulses if the fluid flowing through the feedback path has a permissible velocity vector component, not equal to zero, in a direction which is opposite to any vector component of angular acceleration about that axis. Accordingly, with respect to rotational motion about a longitudinal axis, as shown in FIGURE 5, the maximum modulation for a given angular acceleration occurs when the plane of t e fluid feedback path is perpendicular to the axis of rotation. This is true, even though the axis of rotation may be displaced eccentrically with respect to the rotation of the feedback path.

It is thought that the oscillator illustrated in FIGURES l and 2, when a liquid or a gas is employed as the working fluid, openates as follows:

As the power stream is turned on, the power stream flow initially distributes itself in some asymmetrical flow pattern between the output passages lit and 19. Ordinarily, the power stream flow does not split evenly between the two passages 18 and 19, so that a first output passage, for instance the output passage 18, receives slightly more fluid than the second output passage 19. As the power stream flows across the orifices of the nozzles 15 and 16, the power stream aspirates fluid from the control nozzles 15 and to, lowering the pressure in these control nozzles.

The control nozzle over which the larger proportion or part of the power jet flow passes will lose more fluid by aspiration than the opposite control nozzle and the net effect will be to increase the pressure in the control nozzle having the least flow removed by aspiration, and to decrease the pressure in the control nozzle having more flow removed by aspiration. This effect is cumulative in nature, the flow from the control nozzle initially having the least flow removed by aspiration decreasing, and the flow from the control nozzle initially having the greater flow removed by aspiration increasing, so that the power stream is forced by the pressure differentials between the orifices of the control streams and the power stream to be displaced further into the first output passage initially receiving the greatest amount of fluid. This regenerative action continues until the power stream attaches itself to the sidewall in which the control nozzle at the lower pres sure is located.

The initial small pressure difference across the power stream and the control nozzle orifices, now increased considerably as a result of the power stream attaching to a chamber sidewall, causes the fluid in the feedback loop connecting the control nozzles to thereupon flow from the higher pressure region in one control nozzle to the lower pressure region in the opposite control nozzle, in turn, causing a high pressure wave or front to propagate around and through the feedback loop from, for example, the nozzle 15 to the nozzle 16. As the higher pressure front travels through the loop at its characteristic velocity; that is, the velocity of sound in the fluid employed, it imparts momentum to the fluid in the feedback loop as the front moves through the fluid causing the fluid to move in the direction of travel of the higher pressure front. The high pressure front ultimately issues from the control nozzle 16 towards which it is traveling, followed by the fluid behind the high pressure front which has been caused to travel through the feedback loop in the same direction by the momentum imparted to the fluid by this front. This fluid issuing from the control nozzle displaces, and finally effects complete switching of the power jet into the second output passage 19, in the time it takes for the power stream to detach itself from the wall to which it was hitherto attached.

The aforedescribed cycle continues, producing an oscillating fluid output from the output passages 18 and 19.

From the foregoing, it is believed that some conclusions can be drawn about the behavior of oscillators using liquid as the working fluid as distinguished from gas. In such oscillators, the sonic velocity is very high, but the amount of fluid actually in motion is very low because of the low compressibility of liquids. As a consequence, the time required to develop sutficient flow for power stream switching is relatively long. Thus, the flow velocity rather than the acoustic velocity of the liquid controls the frequency of the oscillator.

When the power stream switches between output passages 18 and 19, it will take time to overcome the inertia 5 of the fluid in the feedback loop. Since this time is longer for denser fluids, the frequency of operation of the type of oscillator under discussion will depend upon the sonic velocity only for low density fluids, or when the mass, and therefore the inertia of fluid in the delay line, is relatively low.

Referring now to FIGURE 5 of the drawings, there is shown a body 40 for mounting the oscillator 10 for rotation about an axis AA, the axis AA being perpendicular to the plane of the half coil 32 and parallel to its axis. The axis AA may, or may not be aligned concentrically with respect to the axis of symmetry CL of the amplifier 11.

Although FIGURE 5 illustrates the amplifier 11 having a feedback coil of one-half convolution, it is understood that this is merely exemplary, and the feedback coil shown in FIGURE 2, for example, could be substituted therefor, as well as any of the configurations previously indicated.

V/ith reference now to FIGURE 2, assume for the purpose of explaining the operation of the system 10 that the mass flow of fluid is initially periodically oscillating between the control nozzles 15 and 16, so that these nozzles are issuing periodic alternating fluid streams for displacing the power stream between the output passages 18 and 19, whereupon symmetrical oscillating output fluid pulses issue from the output tubes 20 and 21. This output will, for example, appear as the pulsed fluid signal illustrated in FIGURE 3. The average velocity of the fluid in the coil 31 and the loop 30 can be regarded as equal to zero since the oscillator is oscillating at equal periodic intervals. If the system 10 is then rotated in the direction of the arrow B, the momentum of the fluid in the coil 31 relative to the coil 31 becomes negligible and the fluid can be regarded as moving in a relatively opposite sense of direction to that of coil rotation, as indicated by arrow B. The control nozzle 16 therefore receives fluid from the coil 31 for an incrementally increased period of time, At, and issues a longer duration control stream which incrementally increases the period of displacement of the power stream into the opposed output passage 18. As a result, an asymmetrical pulse issues from the output tubes 20 and 21, the peak width of the pulse being increased an amount AW, FIGURE 4, corresponding to the increase in angular acceleration of the modulator it The increase in angular acceleration of the modulator It? can therefore be considered equivalent to imposing an acceleration bias to the power stream of the modulator since the power stream is, in effect, biased more into one output passage than the other for the period of acceleration and as long thereafter as the period of acceleration continues.

One complete period of oscillation involves the switching of the power stream from a first output passage into a second output passage and then back into the first output passage. When the power stream switches into the second output passage, the direction of travel of the high pressure front and the direction of rotation of the feedback loop will be the same, so that the time period required for switching the power stream back into the first output passage will decrease an amount At. This is equal to the increase in time At, resulting from the high pressure front traveling in a direction opposite to that of rotation of the feedback loop. Thus, the width of the pulse base will be decreased a differential amount AW equal to the differential increase in width AW of the pulse peak for any one period of oscillation. Therefore, it will be evident that the period or frequency of oscillation is unaffected by the magnitude of angular acceleration of the modulator.

If the modulator It were rotated in a direction opposite to that indicated by the arrow B, and assuming that the power stream is initially flowing into the output pas-sage 18, the pulse peak width will decrease an amount AW, whereas the pulse base will increase a corresponding differential amount, AW, since under this condition the direction of travel of the high pressure front from the control nozzle 16 to the control nozzle 15 is initially opposite that of the direction of rotation of the feedback loop and subsequently in the same direction as the direction of loop rotation.

Thus, the modulator 1% produces pulses that have a constant frequency but which are modulated in width in accordance with the angular acceleration and direction of rotation of the modulator.

If coil 31 is constantly accelerated, the incremental increases in pulse width will be constant. However, if the coil 31 is thereafter rotated at constant velocity viscous effects will continuously reduce the momentum of the fluid in the coil 31 so that the increases in pulse width AW accordingly decrease until the momentum of the fluid in the coil 31 becomes negligible and the pulses become symmetrical, as shown in FIGURE 3. Thus, the mo-dulator 10 is sensitive to angular acceleration in the plane of the coil 31.

Conversely, if the coil 31 is rotated in a direction opposite to that shown by the arrow B the control nozzle will be acceleration biased and again modulated pulses will issue from the output tubes and 21.

The particular means or mechanism by which the system 10 is rotated will ordinarily be merely a matter of choice, and any means which will cause rotation of the system 10 may have its angular acceleration sensed by the system 10. The modulated fluid output signals from the output tubes 20 and 21 may be used as control fluid signals to read out the angular acceleration of body 40, or the fluid signal output may be used to control or operate other types of devices which utilize fluid for their operation or control, as will be evident to those working in the art.

The memory of the modulator; that is, the period during which the fluid is still moving in the delay line after acceleration ceases, increases as a function of the ratio between the diameter, or width, of the delay .line to the length of the delay line. Thus, the shorter the length and larger the diameter of the delay line, the longer the memory of the modulator. The memory feature of the modulator may, for example, be utilized as an indication of the angular velocity of the system embodying the modulator after the angular acceleration has ceased or become negligible.

In FIGURE 6, there is illustrated a negative feedback oscillator. The power stream normally is deflected about its center position axially aligned with the nozzle so as to direct fluid to one or the other of output passages 51 and 52. However, with a loop 53 connected between opposed control nozzles 54 and 56, the mean position of the stream is changed when the device is rotated about the centerline C This fact results from flow of fluid into the interaction region from one of the control nozzles, such as 54, and out of the region through the other control nozzle 56, upon rotation of the device as indicated by arrow 57.

Since the mean position of the power stream is now directed toward the output passage 52, the stream spends more time directed toward this passage than toward passage 51 and pulse width modulation results.

It should be noted that an externally excited oscillator may also be employed. Specifically, the feedback channels may be eliminated and control nozzles 58 and 59 connected across the output terminals of any type of fluid flow producing oscillator. The operation is the same as described above.

In FIGURE 7, an analog amplifier is provided with a loop 61 extending between opposed control nozzles 62 and 63. The mean position of the power stream is again a function of angular rate of rotation about centerline C and the differential in pressures, mass flow, etc, between output channels 64 and 66 becomes a function of angular acceleration.

It should be noted that the loops 31, 32 and 53 (61) may be used interchangeably depending upon the mass flow and inertance desired in the loop.

As stated previously, and in accordance with the teachings of this invention, the feedback loops of conventional relaxation type pure fluid oscillator may also be formed with one or more convolutions, or portions thereof, positioned so that the plane of at least a portion of the feedback path is in the plane of angular acceleration of the oscillator. The feedback fluid signal will t-husly be acceleration biased and the fluid output pulses modulated in accordance with the magnitude and direction of angular acceleration of the oscillator.

While I have described and illustrated several specific embodiments of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A pure fluid pulse width modulator comprising a pure fluid amplifier of the boundary layer type including interaction chamber for receiving fluid streams, a power nozzle for issuing a defined power stream into said interaction chamber, plural output passages for receiving the power stream, a pair of substantially opposed control nozzles positioned to effect displacement of the power stream relative to the output passages by fluid egressing therefrom at an angle with respect to the direction of power stream flow, fluid conveying means connecting said control nozzles and producing alternating fluid pulses in said control nozzles, at least one convolution formed in said conveying means; and means for rotating the modulator about an axis substantially parallel to the axis of the convolution.

2. A pure fluid pulse width modulator comprising a pure fluid amplifier of the boundary layer type, said pure fluid amplifier including a power nozzle for issuing a power stream, an interaction chamber positioned downstream of said power nozzle for receiving said power stream therefrom, output passages located downstream of said interaction chamber for receiving fluid therefrom, at least a pair of control nozzles for issuing control fluid streams, said control nozzles positioned to effect amplified displacement of the power stream between said output passages, fluid conveying feedback means connected to the control nozzles for supplying alternating fluid pulses to said control nozzles, at least one convolution formed in said feedback means, said convolution having an axis of symmetry; and means for rotating the modulator parallel to said axis of symmetry of said convolution.

3. A pure fluid pulse width modulator comprising a pure fluid amplifier of the boundary layer type, said pure fluid amplifier including a power nozzle for issuing a power stream, an interaction chamber positioned downstream of said power nozzle for receiving fluid therefrom, said interaction chamber having an axis of symmetry, plural output passages located downstream of said interaction chamber for receiving fluid therefrom and disposed symmetrically with respect to said axis of symmetry, at least a pair of control nozzles for issuing control streams for effecting amplified displacement of the power stream between said output passages, tube means connected to said control nozzles for producing alternating fluid pulses in said control nozzles, at least one coil formed by said tube means and having an axis perpendicular to the plane of said coil, and means for rotating the modulator about said axis of coil.

A pure fluid system comprising a pure fluid amplifier of the boundary layer type comprising a pair of control nozzles for issuing opposed alternating fluid streams for causing oscillation of fluid output from said amplifier, a tube connecting said control nozzles, and at least one coil formed in said tube, said coil having an axis, and

means for rotating said system parallel to the axis of said coil.

5. A pure fluid system comprising a pure fluid amplifier of the boundary layer type including a pair of control nozzles for issuing alternating fluid streams for causing oscillation of the fluid output from said amplifier, means for converging fluid streams between said nozzles, said means formed with a substantially planar convolution and means for rotating said amplifier about an axis at an angle with respect to the plane of the convolution.

6. A pure fluid pulse width modulator comprising a pure fluid amplifier including an interaction chamber for receiving fluid streams; a power nozzle for issuing a defined power stream into said interaction chamber; plural output passages for receiving the power stream; a pair of substantially opposed control nozzles positioned to effect displacement of the power stream relative to the output passages by fluid egressing therefrom at an angle with respect to the direction of power stream flow; fluid conveying means connecting said control nozzles and producing alternating fluid pulses in said control nozzles; said nozzles and said output passages defining a plane; at least a portion of said fluid conveying means being disposed outside of said plane; and means for rotating the modulator about an axis disposed at an angle with respect to said portion of said fluid conveying means.

7. The pure fluid pulse width modulator according to claim 6 wherein the angle of the axis of rotation with respect to said portion of said fluid conveying means is approximately 90 degrees.

8. A pure fluid system comprising a pure fluid amplifier of the boundary layer type comprising a pair of control nozzles for issuing opposed alternating fluid streams; fluid conveying means connecting said control nozzles and producing alternating fluid pulses in said control nozzles for causing oscillation of fluid output from said amplifier; means for rotating said system about an axis so as to impart an angular acceleration to said system; at least a portion of said fluid conveying means being so disposed that the fluid flowing therethrough has a permissible velocity vector component, not equal to zero, in a direction which is opposite to any vector component of angular acceleration about said axis, whereby the fluid output of said system will be pulse width modulated by the acceleration imparted thereto.

9. A pure fluid pulse width modulator comprising a pure fluid amplifier of the boundary layer type, said pure fluid amplifier including a power nozzle for issuing a power stream, an interaction chamber positioned downstream of said power nozzle for receiving said power stream therefrom, output passages located downstream of said interaction chamber for receiving fluid therefrom, at least a pair of control nozzles for issuing control fluid streams, said control nozzles positioned to eflect amplified displacement of the power stream between said output passages, fluid conveying feedback means connected to the control nozzles for supplying alternating fluid pulses to said control nozzles, at least a portion of a con volution formed in said feedback means, and means for rotating the modulator about an axis disposed at an angle with respect to the plane of convolution.

10. The pure fluid pulse width modulator according to claim 9 wherein said angle is approximately degrees.

11. A pure fluid pulse width modulator comprising a pure fluid amplifier of the boundary layer type including an interaction chamber for receiving fluid streams, a power nozzle for issuing a defined power stream into said interaction chamber, plural output passages for receiving the power stream, a pair of substantially opposed control nozzles positioned to effect displacement of the power stream relative to the output passages by fluid egressing therefrom at an angle with respect to the direction of power stream flow, fluid conveying means connecting said control nozzles and producing alternating fluid pulses in said control nozzles; at least a portion of a convolution formed in said conveying means; and means for rotating the modulator about an axis substantially parallel to the axis of convolution.

12. The pure fluid pulse width modulator according to claim 11 wherein said axis of rotation coincides with the axis of convolution.

13. The pure fluid pulse width modulator according to claim 11 wherein said portion of said conveying means constitutes approximately one-half of a convolution.

14. A pure fluid angular accelerometer for detecting angular acceleration about a particular axis, comprising a pure fluid amplifier including an interaction chamber for receiving fluid streams; a power nozzle for issuing a defined power stream into said interaction chamber; plural output passages for receiving the power stream; a pair of control nozzles positioned on opposite sides of said power nozzle to eflect displacement of the power stream relative to the output passages by fluid egressing therefrom at an angle with respect to the direction of power stream flow; fluid conveying means connecting said con trol nozzles; said nozzles and said output passages defining a plane; and at least a portion of said fluid conveying means including at least a partial convolution disposed outside of said plane and at an angle to the axis of angular acceleration to be detected.

15. The fluid pulse width modulator of claim 14 wherein said partial convolution defines a plane perpendicular to the plane defined by said nozzles and said output passages.

16. The combination according to claim 14 further comprising flow means for oscillating said signal equally to opposite sides of the centerline of said power nozzle in the absence of angular acceleration.

17. The combination according to claim 16 further comprising control means for developing a further differential in pressure across said power stream and wherein said flow means comprises an external source of oscillation.

References Cited by the Examiner UNITED STATES PATENTS 3,016,066 1/1962 Warren 137-8l.5 3,163,048 12/1964 Siegmund et a1. 73-516 3,203,237 8/1965 Ogren 137-815 X 3,205,715 9/1965 Meek 73-516 M. CARY NELSON, Primary Examiner. S. SCOTT, Assistant Examiner. 

1. A PURE FLUID PULSE WIDTH MODULATOR COMPRISING A PURE FLUID AMPLIFIER OF THE BOUNDARY LAYER TYPE INCLUDING INTERACTION CHAMBER FOR RECEIVING FLUID STREAMS, A POWER NOZZLE FOR ISSUING A DEFINED POWER STREAM INTO SAID INTOACTION CHAMBER, PLURAL OUTPUT PASSAGES FOR RECEIVING THE POWER STREAM, A PAIR OF SUBSTANTIALLY OPPOSED CONTROL NOZZLES POSITIONED TO EFFECT DISPLACEMENT OF THE POWER STREAM RELATIVE TO THE OUTPUT PASSAGE BY FLUID EGRESSING THEREFROM AT AN ANGLE WITH RESPECT TO THE DIRECTION OF POWER STREAM FLOW, FLUID CONVEYING MEANS CONNECTING SAID CONTROL NOZZLES AND PRODUCING ALTERNATING FLUID PULSES IN SAID CONTROL NOZZLES, AT LEAST ONE CONVOLUTION FORMED IN SAID CONVEYING MEANS; AND MEANS OF ROTATING THE MODULATOR ABOUT AN AXIS SUBSTANTIALLY PARALLEL TO THE AXIS OF THE CONVOLUTION. 